In order to remove coatings and/or rust from an underlying surface, industry is moving away from the use of chemical stripping agents and towards the use of blasting techniques. With these blasting techniques, abrasive or non-abrasive media or water are blasted onto the surface at high velocity to remove the coating(s) or rust. There are a wide variety of blasting nozzles and blasting media on the market. The most widely used blasting systems use pressurized blasting media, whereas other systems use a suction feed in which the blasting media is fed into a high velocity air stream via suction. Suction feed systems do not typically have as much power as a pressurized blasting media system. Commonly used blasting media includes silica (i.e. sand), plastic, glass or water, but there is also a wide range of specialized blasting media ranging from steel shot, on the one hand, to cornstarch or soy bean media on the other.
In a typical setup, the user holds the blasting nozzle over their shoulder and blasts the media towards the workpiece. The distance that the blasting nozzle is from the workpiece is commonly referred to in the trade as “standoff” distance. The standoff distance is important because it regulates the velocity of the blasting media as it impacts the coated or rusted surface. The angular orientation of the blasting nozzle with respect to the coated or rusted surface is also important because the rate of removal varies significantly with respect to the angle of attack.
Typically, the user aims the high velocity jet containing the entrained blasting material at the surface until the coating or rust is removed at that spot. The user then moves the jet across the surface in an up and down or back and forth motion in order to remove the coating from the surface. Once the coating(s) and/or rust are removed, the user should continue until the underlying surface is properly cleaned, although care should be taken not to damage the underlying surface. In the field, matching templates are used to rate the cleanliness of the surface once the paint and/or rust layers have been removed.
When the user starts a job, the user might not know the thickness of the coating, or the amount of rust, and therefore must guess based on experience and trial and error as to the appropriate standoff distance and orientation angle. If the nozzle is too close or not tilted enough with respect to the surface, the impact of the blasting media may cause pitting to the surface. On the other hand, if the standoff distance is too great or the tilt too large, the blasting media may not have enough impact to remove the coating or rust.
It can be difficult for a person using a blasting nozzle to keep the nozzle at the optimum distance and orientation from the surface in order to properly remove coatings and rust without damaging the underlying surface. This can be especially difficult for novices. The ideal standoff distance and orientation is normally dependent on the type of blasting material, the supplied pressure, as well as the characteristics of the underlying surface and coating. Training and practical experience helps novices improve their skills, however, hands-on training is time-consuming, labor-intensive and expensive. These factors have made training of large groups, such as military personnel or industrial contractors, impractical. As a practical matter, hands-on training tends to limit the number of techniques that can be practiced and evaluated, especially with respect to multiple coatings, and different types of blasting media.
The assignee of the present application is also the assignee of three pending patent applications relating to the use of computer simulation and virtual reality for training and analyzing proper spray painting techniques. The first pending application is application Ser. No. 11/372,714, Publication No. US2007/0209585A1, entitled “Virtual Coatings Application System” by Ebensberger et al., filed on Mar. 10, 2006 and incorporated by reference herein. The virtual coatings application system disclosed in this pending application generally includes a display screen on which is defined a virtual surface (such as a truck door) that is intended to be virtually painted or coated by the user. The user operates an instrumented spray gun controller that outputs one or more signals representing data as to the status of the controls on the spray gun controller, for example, the position of the trigger, the paint flow rate and the pattern fan size. The system also has a motion tracking system that tracks the position and orientation of the spray gun controller with respect to the virtual surface defined on the display screen. Simulation software in the computer, preferably a desktop or laptop PC, generates virtual spray pattern data in response to at least the data from the spray gun controller and the position orientation data received from the tracking system. A virtual spray pattern image is displayed in real time on the display screen in accordance with the accumulation of virtual spray pattern data at each location on the virtual surface. The paint model is preferably based on empirical data collected from actual spray patterns generated for various spray gun settings. The preferred model simulates coverage distribution in an elliptical pattern in which the inner elliptical radii for width and height define an area of constant rate of coverage and the outer elliptical radii for width and height define the outer extent to which the rate of coverage becomes negligible. The total finish flow rate per unit time (i.e. per software timing cycle) is determined by the settings on the spray gun controller as well as its monitored orientation with respect to the virtual surface, and is distributed over the virtual surface via random number generation in accordance with the above-described elliptical distribution pattern. Each location on the virtual surface has an associated alpha channel which controls transparency of the coating at that location (e.g. pixel) based on accumulation of virtual spray at the given location, thus realistically simulating fade-in or blending for partial coverage on the virtual surface.
Another pending application, application Ser. No. 11/539,352, Publication No. US2007/0209586A1, entitled “Virtual Coatings Application System” filed on Oct. 6, 2006, assigned to the assignee of the present invention and also incorporated herein by reference, further discloses an immersive system in which the user wears a head-mounted display unit that virtually places the user in a three-dimensional virtual spray painting environment. The three-dimensional virtual environment provided to the user by the head-mounted display contains a three-dimensional depiction of the virtual surface to be painted, and also preferably contains a depiction of a spray gun simulating the position and orientation of the instrumented spray gun controller with respect to the virtual surface. In this system, the tracking system also tracks the position and orientation of the head-mounted display unit in order to provide the appropriate perspective to the user in the immersive environment. In this system, it is especially useful for the user controls to be accessible from within the immersive environment so that the user does not have to remove the head-mounted display unit. This is accomplished by providing menu icons within the immersive environment that can be activated and controlled by the instrumented spray gun controller.
Another relevant copending application, application Ser. No. 11/563,842 entitled “Virtual Coatings Application System With Structured Training And Remote Instructor Capabilities”, filed on Nov. 28, 2006, assigned to the assignee of the present invention and also incorporated herein by reference, relates to software that facilitates structured training of planned lesson curriculum and enhanced network capabilities that allow students to view an instructor demonstrating technique in a remote location. Spray painting virtual reality training systems commercially offered by the assignee often include the features described in all three of these copending patent applications, although some systems do not incorporate all of the features.